Belt drives: "If it aint broken, why fix it?"

'Spokesman' is the agent provocateur columnist in the back of BikeBiz magazine. In the October issue he wrote:

"The chain, the driving force of the bicycle, cannot be improved. I find it incredible that companies such as Orange (and Gates and Spot Bikes) spend thousands on research and development, trying to improve on the tried-and-tested, highly-efficient bicycle chain. If it ain’t broken, why fix it?"

This comment was picked up by a contributor to the trade-only BikeBiz.com forum:

"Personally I'm all for innovation and in my opinion an oily dirty chain is the thing most commuters hate to touch."

This then led to a verbal tennis match as the pros and cons of carbon belt drives were discussed by members of the bicycle industry. BikeBiz.com has run two stories on the Gates Corporation's PolyChains, here and here, but not all correspondents on the forum appear to have read them.

A regular correspondent who has read them and who has ridden the prototype PolyChain bikes from Orange is Ben Cooper of Glasgow bike shop Kinetics. He said:

"Until I'd actually ridden the Orange bike, I definitely thought that the roller chain was about as good as bike transmission could get - but this new generation of belt drives is very exciting. They're clean, very, very efficient, and don't need regular maintenance.

'Bikeshed' disagreed: "The belt will have its place, commuter/tarmac bikes, but I don't believe they will ever be any good off-road in the mud and cack."

Cooper replied: "I think that's exactly where they'll be brilliant - the mud just squishes out the side or between the teeth on the pulley."

Lloyd Townsend of Ison Distribution then weighed in:

"What worries me is the required tension. I don't know how tight it really is but your classic fan belt on a car has to be silly tight not to slip. I hear of many hub bearing troubles, and many of them are caused by drive chains being overtightened. Freewheel systems/bearings especially are not usually designed to handle overtight chains. Hence, I would be unsure about the headaches that may arise in other components with a tightly tensioned transmission belt (or chain) drive system."

Marten Gerritsen of M-Engineering in the Netherlands begged to differ:

"Fanbelts rely on friction, and will always slip as the inside and the outside of the belt run at the same speed, but on a different diameter of the same pulley. A toothed belt only needs tension to prevent it from climbing up the teeth."

Cooper said: "The ones I've seen have been about as tight as a singlespeed chain - I've got a v-belt drive Birdy here, and the belt on that is far less impressive. I think it's the combination of a zero-stretch toothed belt and the cutaway pulleys that are the key to this working - I was very unconvinced until I tried Michael's demo bike, but now I'm a convert.

DocB wrote: "One of the real up sides of the chain drive is its flexibility and that is not just to allow it to go round corners. The same bits can be used on every thing from a fixed wheel single speed, through high geared road bikes and wide range geared mountain bikes to recumbants with miles of drive system. You can solve most peoples drive problems for most bikes with a relatively small stock of components and simple tooling

"Principal downsides of the chain drive is that chains need regular lubrication, get filthy, and wear.

"Strikes me that the belt drive is just the opposite! Gets rid of the downsides of the chain drive but simultaneously gets rid of the up sides.

"So like most things where there are alternatives, there are times when one will provide the better design solution and times when the other will do it."

Want to hear more about belt-drives? Listen to this podcast interview with David Arthur, a senior engineer at Gates Corporation, and Michael Bonney of Orange. It's available on iTunes and as an MP3 download.